During a radionuclide dispersion event, a radionuclide dispersion event being a release of radioactive contaminants through an act of malice, nuclear reactor accident, or otherwise, large swaths of area and equipment may be contaminated. An exemplary act of malice is the activation of a radiological dispersal devise, commonly known as a “dirty bomb,” where an amount of radioactive material is used to maliciously contaminate people, equipment, and/or the environment without a nuclear explosion. “‘Dirty Bombs’: Technical Background, Attack Prevention and Response, Issues for Congress” J. Medalia, 7-5700, Jun. 24, 2011, Congressional Research Service.”
In the course of such a radiological dispersion event, radionuclide contaminants may be spread across large areas. Surfaces of critical infrastructure and equipment such as fire houses, medical facilities, and emergency response tools and equipment onto which the radionuclide contaminants rest may become contaminated, in turn compromising response efforts by emergency response officials. In addition, some public services such as drinking and wastewater treatment, electrical power distribution, etc. may be disrupted. In such an event, it is important to deploy mitigation efforts to reduce levels of radioactive contaminants by removal or decontaminating certain areas in order to restore response activities and public services. Disclosed herein is a method and system useful for the mitigation of radionuclide contamination from surfaces bearing radionuclide contaminants. The method and system are particularly useful to rapidly return components such as fire-fighting equipment to service following a radionuclide dispersion event while also avoiding further radionuclide contaminant spread beyond the original deposition area and minimizing the amount of additional materials contaminated during the mitigation processes. The method and system are rapidly deployable, cost-effective measures to mitigate critical infrastructure and equipment for the purpose of restoring that infrastructure and equipment to operational activities after a radiological release.
Application of the radionuclide contaminant mitigation method or utilization of the system has the potential to reduce the level of radionuclide contaminants on surfaces. They may be performed on both a small scale as on tools, detectors, and personal protective equipment, as well as on a large scale as would be the case with critical infrastructure or equipment. Thus, by performing the method or utilizing the system, the exposure to radiation by emergency workers, responders, and the general population who are in close proximity to those surfaces is lessened. The method comprises applying a carrier solution comprising a cation onto a surface bearing a radionuclide contaminant, such that the radionuclide contaminant enters the solution to form a laden solution. The method then employs contacting the radionuclide contaminant laden solution with solid sequestering agents that bind to and immobilize at least a portion of the radionuclide contaminant. In providing another binding material, the mobility of the radionuclide contaminant through the environment is lessened as a whole.
Mitigation with respect to the method refers to the removal of at least a portion of the radionuclide contaminant from a bearing surface. Mitigation typically occurs shortly after a radiological dispersion event. This removal is necessary in order to restore critical infrastructure such as fire houses to a level that the infrastructure can be utilized. Note that mitigation differs from decontamination; a long term activity designed to clean-up the contaminated infrastructure to acceptable near background levels. Thus, these mitigation methodologies may not be as effective in decreasing radionuclide contaminant radiation levels to background level as those methodologies used for final decontamination. Nevertheless, during mitigation, speed and economy at which methodologies or systems can be deployed and completed may be of equal importance relative to effectiveness, and may also impact the effectiveness of follow-on decontamination for longer term recovery.
Radionuclide contaminants include the isotopes of stable elements that produce alpha, beta, or gamma radiation through their radioactive decay. Radioisotopes are rarely available in quantities sufficient to cause harm outside of highly restricted areas such as nuclear reactors. Thus, while there are approximately 3,715 different identified radionuclides, there is a relatively small number likely to be spread in a radiological dispersion event based on quantities available, key physical and chemical characteristics such as half-life, and decay activity. Those radioisotopes of greatest concern are listed in Table A below. Of those listed in Table A, the radioisotopes available most likely to be in civilian control and thus most likely to be spread by a radiological dispersion event include Co-60, Cs-137, Ir-192, Sr-90 and Am-241.
TABLE AMode ofRadioisotopeDecayAm-241αCd-109x-rayCf-252αCo-60β-γCs-137β-γCs-134β-γFe-55x-rayGd-153x-rayHo-166β-γI-125x-ray-γI-131β-γIr-192β-γKr-85β-γLu-177β-γNi-63βP-32βP-33βPd-109β-γS-35βSe-75γSr-90βW-188β
Radionuclide contaminants may be in a variety of physical forms such as powders, clad with ceramics (reactor fuel rods), etc. The most likely forms are cesium chloride, cesium oxides, cesium alumino-silicates, other cesium ceramic materials, strontium fluoride, strontium oxides, strontium titanates, cobalt metal or metal alloy, iridium metal or metal alloy, and mixed fission product and actinide nitrates. Of these, the alumino-silicates, ceramics, titanates, metals and metal alloys are insoluble in water and would likely persist as particulate material after dispersion into the environment. As such, decontamination would involve the physical removal of particles from contaminated surfaces rather than chemical desorption of radioactive contaminants from surface chemical sorption sites.
The cesium chloride and oxides, and the strontium fluorides and oxides are soluble in aqueous solutions. After dispersion during a radionuclide dispersion event, these radionuclide contaminants can dissolve in the water present within a building material (e.g., pore water), from a precipitation event, or from contact with bulk water (e.g., fire hose, ocean spray). This dissolution of the radionuclide contaminants allows them to easily become chemically bonded onto the surface material, primarily through ion exchange reactions with the surface. In terms of chemical form, those radionuclides that persist as small particulate are easier to mitigate than those that have dissolved in water and reacted chemically with the surface.
As illustrated in FIG. 1, the chemical and physical characteristics of the surface on which the radionuclide contaminant rests has a significant impact on the percentage of radionuclide contaminant that can be mobilized by the carrier solution. Asphalt, brick, limestone, granite, and concrete are representative of porous urban construction materials present in critical infrastructure such as roadways, hospitals, and public works facilities. Different surfaces frequently lead to different sorption mechanisms and dissimilar surfaces promote mobilization of the radionuclide contaminants while using the method or system.
The mitigation of radionuclide contamination as performed by the method and system, when put into the context of the overall response to a radiological dispersion event, makes a significant difference in the outcome in several areas. The resulting reduction allows emergency responders to conduct operations for longer periods of time by reducing their cumulative dose of radiation while working in a “hot” zone. This is critical in the early phases of a radiological dispersion event when the number of first responders will be limited. In an exemplary radiological dispersion event where there would be a release of 1,000 Curies of Cesium-137 (50 grams) over an urban area of 2.10 km2, a population of 38,000 individuals if not removed from the area would experience an increase of 233 cases of cancer including 159 fatal cases, from a first year of exposure alone. “‘Dirty Bombs’: Technical Background, Attack Prevention and Response, Issues for Congress” J. Medalia, 7-5700, Jun. 24, 2011, Congressional Research Service.”
During emergency response operations, a 50% reduction of a radionuclide contaminant such as Cs-137 from the surface of a piece of equipment and the resulting reduction in radiation exposure will allow emergency response workers to remain in the area twice as long performing twice as much life-saving activity at a time when qualified workers represent a scarce resource. The lower exposure also benefits workers involved in restoring the area to its original condition during late-phase recovery activities by removing the easily mobilized radionuclide contaminants from the area before more aggressive decontamination procedures are implemented. Further, reducing the contamination level even 30% at the beginning of a radiological dispersion event response may result in significant savings later, because the longer the radionuclide contaminant remains in contact with some common materials, the more aggressive the approach needed to decontaminate them—for example grinding off the surface may be necessary, which can be logistically more challenging and destructive and further results in a higher cumulative radiation dose exposure to the work force. Finally, reduction in radionuclide contaminants via this method correlate to potentially significant reductions in the volumes of radiologically impacted wastewater. Namely, the method immobilizes and allows the removal of radionuclide contaminants preventing their spread through a watershed.